In this work, we propose to develop a prototype electrical stimulation system for use as an exercise system for combined strength/endurance training and as a therapeutic tool in motor retraining paradigms. The target populations for this device are: 1) individuals with spinal cord injury (SCI) who are interested in improving their physical fitness through electrically stimulated lower-extremity exercise, 2) individuals with SCI who seek to develop or maintain adequate muscle strength that will allow routine use of an FES system for standing, and 3) individuals with incomplete thoracic-level injury who have the potential to regain voluntary lower extremity motor fitnction through motor retraining therapy. The proposed system will supplement commercially-available exercise equipment with an adaptive electrical stimulation system. With the subject in a head-up tilt posture, the lower extremity extensor muscles will be stimulated to generate a deep-knee-bend type of movement in a cyclic manner. The mechanical structure of the exercise equipment will provide safety and stability while the adaptive electrical stimulation system generates a stimulation pattern to produce the desired movement. In Phase I we will demonstrate feasibility by developing a prototype and by performing initial experimental tests on a small sample of human subjects with spinal cord injury. In Phase II we will focus on refining the prototype and evaluating the ability of the device to provide health benefits through electrically stimulated lower-extremity exercise. PROPOSED COMMERCIAL APPLICATION: The target price for the proposed device will $1800-$2500. This price would be substantially lower than competing products (FES cycle ergometers) that are commercially viable. The initial market to be targeted will be PT clinics for use with patients with SCI. As proposed, the device will also be a viable option for home use by some individuals with SCI. Other potential applications of this device will be for strength training and motor retraining in stroke patients and possibly for strength training in patients with orthopedic problems at the knee.